Compositions of random copolymers of propene containing an α-olefin as comonomer

ABSTRACT

Semicrystalline polyolefin composition comprising copolymers a), b) and c) of prolylene with at least one comonomer selected from C 4 -C 10 α-olefins, where the total content of recurring units from the said comonomer, referred to the composition, is equal to or higher than 6% and teh respective percentages representing the content of said recurring units in each one of the copolymers a), b) and c) are different from each other, said difference being of at least 1 unit.

The present invention concerns compositions of random copolymers ofpropylene with one or more C₄-C₁₀-α-olefins, and the process to obtainthe said compositions. The present invention also relates to articlesproduced by using the cited compositions.

Articles whose production requires the use of high temperatures can beprepared with the polyolefin compositions of the present invention. Forexample, certain types of laminate articles, i.e. sheet and film,require such an operative condition. As a particular example, the saidcopolymer compositions are suitable for the production of metallizedarticles, more in particular metallized films. The films can be eithermonolayer or multilayers. The said compositions can, therefore, beuseful for the production of metallized single-layer and multilayerfilms.

Articles produced with the compositions of the present invention areparticularly suitable for being employed in the food industry because oftheir low content of component soluble in xylene at room temperature.Therefore, the said articles can be used in the food packaging field.

Polyolefin compositions comprising a mixture of two or three copolymersof propylene with an α-olefin, mainly 1-butene, are already known. Thesaid prior art compositions are suitable for the production oflow-temperature heat-sealable films.

For example, U.S. Pat. No. 4,211,852 describes a thermoplastic olefinresin composition made up of a poly(propylene-co-butene-1) with at least15 mole % of recurring units deriving from 1-butene and a copolymer ofpropylene with ethylene or 1-butene containing up to 10 mole % ofrecurring units deriving from the comonomer. However, in examples thecompositions made up of two copolymers do not contain two polymers ofthe type poly(propylene-co-butene-1) and the 1-butene content in thepoly(propylene-co-butene-1) is about 35% by weight.

European patent application 560 326 also describes a thermoplasticolefin resin composition comprising a random poly(propylene-co-butene-1)with from 1 to 10 wt % of recurring units deriving from 1-butene and arandom poly(propylene-co-butene-1) containing from 15 to 40 wt % ofrecurring units deriving from 1-butene.

European patent application 719 829 describes polyolefin compositionscomprising a mixture of three copolymers of propylene with an α-olefin,mainly 1-butene. At least one copolymer contains a high amount ofcomonomer (25% by weight or more). Films prepared with the describedcompositions have low values of heat-sealing temperature as shown by theworking examples wherein the films have a value of the heat-sealingtemperature of 92° C. or less.

Although the cited prior art compositions have a high meltingtemperature, they are not suitable for being metallized. The maindrawback of the said compositions is due to a too high amount of polymerfraction with a low crystallinity thanks to which the films obtainedfrom the said prior art compositions are low-temperature heat-sealable.

The applicant has now found new compositions that have a high meltingtemperature and VICAT value. The said properties enable the polymer tobe subjected to high temperatures such as those required inmetallization process.

A particular advantage of the copolymer compositions of the presentinvention is that they have a low solubility in xylene at roomtemperature and can have a good transparency. The said properties areparticularly desirable in the food industry.

The compositions of the present invention, moreover, have a rather highrigidity. Thanks to the said property, films with a homogenous thicknessare produced.

Therefore, the present invention provides a semicrystalline polyolefincomposition comprising (all percentages by weight):

a) 25-40%, preferably 28-38%, of a random copolymer of propylene with atleast one comonomer selected from C₄-C₁₀, α-olefins, containing from 2to 10% of recurring units deriving from the comonomer;

b) 25-40%, preferably 26-36%, of a random copolymer of propylene with atleast one comonomer selected from C₄-C₁₀α-olefins, containing from 10 to20% of recurring units deriving from the comonomer;

c) 25-40%, preferably 28-38%, of a random copolymer of propylene with atleast one comonomer selected from C₄-C₁₀α-olefins containing from 6 to12% of recurring units deriving from the comonomer;

where the total content of recurring units from the said comonomer,referred to the composition, is equal to or higher than 6% and therespective percentages representing the content of the said recurringunits in each one of copolymers a), b) and c) are different from eachone of the other two, said difference with respect to the percentage ofrecurring units in each one of the other two copolymers being of atleast 1 unit, preferably 1.5 units.

From the above definitions it is evident that the term “copolymer”includes polymers containing more than one kind of comonomers.

Examples of said C₄-C₁₀α-olefins are 1-butene, 1-pentene, 1-hexene,1-octene and 4-methyl-1-pentene. Particularly preferred is 1-butene.

The preferred semicrystalline polyolefin compositions are those wherethe comonomer of copolymers (a), (b) and (c) is the same.

The said composition has, typically, a seal initiation temperature (SIT)from 110° C. to 120° C. The VICAT value is generally from 115 to 140°C., preferably 125-135° C.

The said composition, moreover, has generally values of heat distortiontemperature (HDT) ranging from 65 to 75° C.

Moreover it has generally values of flexural elastic modulus rangingfrom 900 to 1300 MPa, preferably 950-1250 MPa. The haze value isgenerally 40% or less determined on a 1 mm-thick plaque. The melt flowrate (condition L) value is generally from 0.1 to 100 g/10 min. Theabove properties are determined according to the methods described inthe examples.

The composition of the present invention can by prepared by the knownmethods.

One method is by mechanically blending of copolymers (a), (b) and (c) inthe molten state. The blending process is, therefore, carried out at themelt temperature of the copolymers or above.

The preferred method is by way of sequential polymerisation of themonomers in the presence of a catalyst, such as stereospecificZiegler-Natta catalysts.

The sequential polymerisation is carried out in at least three separateand subsequent stages, wherein copolymers (a), (b) and (c) of thepresent invention are prepared. In each stage subsequent to the firststage the polymerisation takes place in the presence of the polymerobtained and the catalyst used in the preceding stage. It is preferredto prepare first the random copolymer containing the lowest amount ofcomonomer and than the other two copolymers.

The polymerisation process can be carried out in liquid phase, in thepresence or absence of inert solvent, or in gas phase, or using mixedliquid and gas phases. Preferably the polymerisation is carried out ingas phase.

The regulation of the molecular weight is done by using knownregulators, preferably hydrogen.

The polymerisation can be preceded by a prepolymerisation step where thecatalyst is caused to contact with small quantities of olefins.

The previously said Ziegler-Natta catalysts comprise a solid catalystcomponent and a cocatalyst. The solid catalyst component comprises atitanium compound having at least one titanium-halogen bond and anelectron-donor compound (internal donor), supported on a magnesiumdihalide in active form. The magnesium dihalide support is preferably inthe form of spheroidal particles having a narrow particle sizedistribution.

The internal donor is generally selected from ethers, ketones, lactones,compounds containing N, P and/or S atoms and esters of mono- anddicarboxylic acids. Particularly suitable electron-donor compounds arephthalic acid esters, such as diisobutyl, dioctyl, diphenyl andbenzylbutyl phthalate.

Other electron-donor compounds particularly suitable are 1,3-diethers offormula:

(R^(I))(R^(II))C(CH₂OR^(III))(CH₂OR^(IV))

wherein R^(I) and R^(II) are the same or different and are C₁-C₁₈ alkyl,C₃-C₁₈ cycloalkyl or C₇-C₁₈ aryl radicals; R^(III) and R^(IV) are thesame or different and are C₁-C₄ alkyl radicals; or are the 1,3-diethersin which the carbon atom in position 2 belongs to a cyclic or polycyclicstructure made up of 5, 6 or 7 carbon atoms and containing two or threeunsaturations.

Ethers of this type are described in published European patentapplications 361493 and 728769.

Representative examples of the said diethers are2-methyl-2-isopropyl-1,3-dimethoxypropane.2,2-disobutyl-1,3-dimethoxypropane,2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane,2-isopropyl-2-isoamyl-1,3-dimethoxypropane,9,9-bis(methoxymethyl)fluorene.

The preparation of the above mentioned solid catalyst component iscarried out according to various methods.

For example, a MgCl₂.nROH adduct (in particular in the form ofspheroidal particles) wherein n is generally from 1 to 3 and ROH isethanol, butanol or isobutanol, is reacted with an excess of TiCl₄containing the electron-donor compound. The reaction temperature isgenerally from 80 to 120° C. The solid is then isolated and reacted oncemore with TiCl₄, in the presence or absence of the electron-donorcompound, after which it is separated and washed with aliquots of ahydrocarbon until all chlorine ions have disappeared.

In the solid catalyst component the titanium compound, expressed as Ti,is generally present in an amount from 0.5 to 10% by weight. Thequantity of electron-donor compound which remains fixed on the solidcatalyst component generally is 5 to 20% by moles with respect to themagnesium dihalide.

The titanium compounds which can be used for the preparation of thesolid catalyst component are the halides and the halogen alcoholates oftitanium. Titanium tetrachloride is the preferred compound.

The reactions described above result in the formation of a magnesiumhalide in active form. Other reactions are known in the literature,which cause the formation of magnesium halide in active form startingfrom magnesium compounds other than halides, such as magnesiumcarboxylates.

The active form of magnesium halide in the solid catalyst component canbe recognized by the fact that in the X-ray spectrum of the catalystcomponent the maximum intensity reflection appearing in the spectrum ofthe nonactivated magnesium halide (having a surface area smaller than 3m²/g) is no longer present, but in its place there is a halo with themaximum intensity shifted with respect to the position of the maximumintensity reflection of the nonactivated magnesium dihalide, or by thefact that the maximum intensity reflection shows a width at half-peak atleast 30% greater than the one of the maximum intensity reflection whichappears in the spectrum of the nonactivated magnesium halide. The mostactive forms are those where the above mentioned halo appears in theX-ray spectrum of the solid catalyst component.

Among magnesium halides, the magnesium chloride is preferred. In thecase of the most active forms of magnesium chloride, the X-ray spectrumof the solid catalyst component shows a halo instead of the reflectionwhich in the spectrum of the nonactivated chloride appears at 2.56 Å.

The cocatalyst is generally an Al-alkyl compound alone or combined withan electron-donor compound (external donor).

The Al-alkyl compound is generally of the trialkyl aluminium type, suchas Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear of cyclicAl-alkyl compounds containing two or more Al atoms bonded by way of O orN atoms or SO₂, SO₃, and SO₄ groups.

Some examples of these compounds are:

(C₂H₅)₂Al—O—Al (C₂H₅)₂;

(C₂H₅)₂Al—N(C₆H₅)—Al (C₂H₅)₂;

(C₂H₅)₂Al—SO₂—Al(C₂H₅)₂;

CH₃ [(CH₃)Al—O]_(n)—Al(CH₃)₂;

—[(CH₃)Al—O—]_(n)

where n is a number from 1 to 20.

One can also use AlR₂H compounds, and AlR₂OR′ compounds, where R is analkyl radical having from 1 to 6 carbon atoms, and R′ represents an arylradical substituted in one or more positions.

The Al-alkyl compound is generally present in such amounts that theAl/Ti ratio ranges from 1 to 1000.

The external electron-donor compound can be selected from esters ofaromatic acids (such as alkyl benzoates), heterocyclic compounds (suchas 2,2,6,6-tetramethylpiperidine, and 2,6-diisopropylpiperidine) andparticularly silicon compounds containing at least one Si—OR bond (whereR is a hydrocarbon radical). Some examples of silicon compounds are(t—C₄H₉) ₂Si(O CH₃)₂,(C₅H₉)₂Si(O CH₃)₂,(C₆H₁₁)₂Si(O CH₃)₂,(C₆H₁₁)(CH₃)Si(O CH₃)₂ and (C₆H₅)₂Si(O CH₃)₂.

The 1,3-diethers of formula (I) can also be used advantageously asexternal electron-donor compounds. In the case where the internalelectron-donor compound is one of the 1,3-diethers of formula (I), theexternal electron-donor compound can be omitted.

The compositions of the present invention can also contain additivescommonly employed in the art, such as antioxidants, light stabilisers,heat stabilisers, pigments and so on.

As previously said, the compositions of the present invention areparticularly useful for the preparation of laminate articles, i.e. filmsand sheets. Due to the features of the polymer compositions, metallizedlaminate articles, in particular films, can be produced. Films aregenerally characterised by a thickness of less than 100 μm, while sheetshave a thickness equal to or higher than 100 μm.

The films of the present invention can be cast or, preferably,bioriented.

The films and sheets can be single-layer or multilayer.

The multilayer film or sheet has at least one cast or bioriented layercomprising the composition according to the present invention. The layerthat comprises the composition of the present invention can be an outerlayer or an inner layer.

The further layer(s) can comprise olefin polymers or other polymers. Thepreferred olefin polymers are propylene polymers. The said further layercan comprise a polymer having low-temperature heat-sealing properties,for example. A practical example of the multilayer film with the saidproperties is a triple-layer film having an ABC-type structure whereinone of the outer layers comprises the composition according to thepresent invention. The middle layer can be a crystalline propylenehomopolymer. The other outer layer can be a random copolymer ofpropylene with a low amount (less than 10% by weight) of recurring unitsderiving from ethylene and/or butene-1.

The films of the present invention can be prepared by known methods,such as extrusion, calendering and bubble.

A further object of the present invention is a metallized laminatearticle, sheet or, preferably, film. Both the said single-layer ormultilayer laminate articles can be subjected to metallization process.Where a multilayer laminate article is metallized, an outer layer ismade of the composition according to the present invention.

Where the laminate article is metallized, for example, the process formetallizing is carried out, for example, by subliming a metal on thesurface of the film according to the known methods. The used metalgenerally belongs to the groups I B to III B of the Periodic Table, suchas aluminium and zinc.

Another object of the present invention is a multilayer laminate articleobtainable by extrusion lamination of a polymer on the layer comprisingthe polymer composition of the present invention. The said layer can bemetallized as well as non-metallized. The polymer used in the extrusionlamination process has, preferably, a melting temperature equal to orless than 150° C., for example polyethylene and polyethyleneterephthalate.

The metallized films of the present invention have a good barriereffect. The said advantageous effect is due to the composition of thepresent invention that enables a good adhesion of the metal to thepolymer layer.

The following examples illustrate but do not limit the method ofpreparation and the characteristics of the composition of the presentinvention.

The data shown in the tables are obtained by using the followinganalytical methods.

Molar ratios of the feed gases: determined by gas-chromatography.

1-butene content: determined by I.R. spectroscopy.

Xylene soluble fraction: 2.5 g of polymer are dissolved in 250 ml ofxylene at 135° C. under agitation. After 20 minutes the solution isallowed to cool to 25° C., still under agitation, and then allowed tosettle for 30 minutes. The precipitate is filtered with a filter paper,the solution evaporated in nitrogen flow, and the residue dried undervacuum at 80° C. until constant weight is reached. Thus one calculatesthe percent by weight of polymer insoluble in xylene at ambienttemperature (i.e., 25° C.).

Melt flow rate (MFR“L”): determined according to method ASTM D 1238,condition L.

VICAT: determined according to method ISO 306.

HDT: determined according to method ISO 75.

Flexural elastic modulus: determined according to method ASTM D 790.

RCI IZOD impact strength: determined according to method ISO 180/1A.

Rockwell R hardness: determined according to internal method MA 17013,available upon request. A Durometer Galileo A-200 instrument is used. A6 mm-thick specimen having sides of 12.7 mm is cut from an injectionmoulded plate.

 The test is carried out at 23° C.; 50% is the relative humidity. A loadof 588.4 N is applied to the specimen for 15 seconds. The load isspherical punch-shaped. The diameter of the spherical punch is of 12.7mm. After removing one waits 1 seconds before reading the value ofhardness on the scale of the durometer. At least 5 tests are performedat different points in the specimen.

 The Rockwell hardness alpha (R_(α)) is calculated with la followingformula:

R _(α)=150−(d _(h) −d _(m))

 wherein d_(h) is the value read on the scale of the durometer and d_(m)is the elastic constant of the durometer.

Fish eyes: determined according to internal method MTM 17108E, availableupon request. A 50 μm-thick film specimen is cut from a film produced bya Bandera 45 extruder equipped with a film drive unit and chill rolls(Dolci.) The film specimen is inserted in a specially provided slot of aprojector (projector Neo Solex 1000 with a lamp of 1000 W and objectiveNeo Solex F 300 equipped with apparatus for collecting the film). Thenthe film specimen is examined on the wall-chart by counting the numberof gels and by noting their dimension.

WVTR water vapour: determined according to internal method MA 18073,available upon request. The test is carried out on a film specimen.

 The film specimen is fixed on a small stainless steel vessel (diameter:59 mm, high: 37 mm) containing 5 ml of distilled water. After weightingthe said vessel, it is turned upside-down so that the water comes intocontact with the film and placed in a room at 23(±1)° C. and 50(±5)% ofrelative humidity at least for 120 hours. The vessel is weighted every24 hours.

 The permeability coefficient of the film to the water vapour iscalculated by using the following formula

(G·s)/(a·t)

 wherein G is measured in grams and is the average decrease of theweight of water every 24 hours; s is the thickness of the film; a is 1m²; and t is 24 hours.

OTR oxygen: determined according to internal method MA 17275, availableupon request. The test is carried out on a film equal to the one used inthe WVTR water vapour test. The film specimen having diameter about of75 mm is cut from a film. The specimen is previously kept in a dryer at23° C. under vacuum (about 1 Pa, i.e 0.01 mbar) for 24 hours.

 The specimen is placed in the middle of a closed steel vessel so thatthe vessel is dived into two rooms. The air pressure is reduced under0.1 Pa (0.001 mbar) in the vessel using a vacuumeter Datametrics type1500. Then the oxygen is introduced in one of the rooms until a pressureof 0.05 MPa (0.5 bar); the oxygen pressure is measured by an Edward EPV251 manometer. Afterwards the pressure of the other room is measured atregular intervals of times until a regular increase of pressure isobserved.

 After calculation of linear regression line based on the experimentalpressure values, the coefficient of permeability (CP) of the film to thegas is calculated by using the following formula:

CP=V·[dP(t)/dt]·[273/(273+T)]·76⁻¹·(L/A)·P ₁ ⁻¹

 wherein V is measured in ml and is the volume of the vessel; P=pressureof the filtered gas; [dP(t)/dt]=angular coefficient of the interpolationline; T is measured in ° C. and is the temperature at which the test iscarried out; L=thickness of the sample; A=surface of the samplesubjected to the gas flow; P₁=pressure of the gas put in; t=time.

Haze: determined according to method ASTM D 1003.

Gloss: determined according to method ASTM D 2457.

Melting temperature: determined by DSC (Differential ScanningCalorimetry).

Seal initiation temperature (SIT): determined by preparing 50 μm-thickfilms by extruding the compositions of the examples at about 200° C.Each film thus obtained is laid over a plaque of polypropylene having axylene-soluble of 4% by weight, melt flow rate of 2 g/10 min. Theoverlapped film and plaque are bonded in a plate-press at 200° C. with aload of 9000 kg. The said load is maintained for 5 minutes. Theresulting bonded test pieces are then stretched six times their lengthand width using a TM LONG film stretcher, thus obtaining films of athickness of about 20 μm. 5×10 cm specimens are obtained from the saidfilms. The sealing values are obtained by applying a 200 g load toheat-sealed samples. For each measurement two of the above specimens areoverlapped with the heat-sealable layers, made up of the compositions ofthe examples, touching each other. The said overlapped specimens arethen sealed along the 5 cm side using a Xentinel combination laboratorysealer model 12-12 AS. The sealing time is 5 seconds, the pressure about0.12 MPa (1.2 atm) and the width of the seals 2.5 cm. The sealingtemperature is increased by 2° C. for each sample to be measured. Thesealed samples are then cut to obtain 2.5×10 cm strips, whose unsealedends are attached to a dynamometer, and the minimum seal temperaturewhere the seal does not break when a 200 g load is applied isdetermined. This temperature represents the seal initiation temperature.

EXAMPLES 1-2 AND COMPARATIVE EXAMPLE 1C

The compositions are prepared by sequential polymerisation, i.e. thepolymerisation is carried out in continuous in a series of reactorsequipped with devices for the transfer of the product from one reactorto the one immediately next to it.

The catalyst used in polymerisation is a highly stereospecificZiegler-Natta catalyst comprising a solid component supported onmagnesium chloride, containing about 2.5% by weight of titanium anddiisobutylphthalate as internal electron-donor component. The solidcatalyst component is prepared by analogy with the method described inthe examples of European published patent application 674991.

During polymerisation the gas phase is continuously analysed bygaschromatography in order to determine the content of propylene,1-butene, hydrogen and propane. The above mentioned gasses are fed insuch a way that during the course of the polymerisation theirconcentration in gas phase remains constant.

Before introducing the catalyst system into the polymerisation reactors,the above solid catalyst component is contacted at 20° C. for 9 minuteswith Al-triethyl (TEA) and dicyclopentyldimethoxysilane (DCPMS) inliquid propane. The TEAL/solid catalyst weight ratio is 10 and theTEA/DCPMS ratio is 4.

The above catalyst system is then transferred into a reactor containingan excess of liquid propylene and propane to carry out prepolymerisationat 25° C. for 30 minutes before introducing it into the firstpolymerisation reactor.

Into a first gas phase polymerisation reactor apoly(propylene-co-butene-1) (copolymer (a)) is produced by feeding in acontinuous and constant flow the prepolymerised catalyst system,hydrogen (used as molecular weight regulator) and propylene and 1-butenemonomers and propane in the gas state.

The copolymer produced in the first reactor is discharged and, afterhaving been purged of unreacted monomers, is introduced in a continuousflow into the second gas phase reactor together with quantitativelyconstant flows of hydrogen, propylene and 1-butene and propane in gasstate.

The copolymer produced in the second reactor (copolymer (b)) isdischarged and, after having been purged of unreacted monomers, isintroduced in a continuous flow into the third gas phase reactortogether with quantitatively constant flows of hydrogen, propylene and1-butene and propane in gas state, to produce copolymer (c).

The polymer particles exiting the third reactor are subjected to a steamtreatment to remove the reactive monomers and volatile substances andthen dried.

The polymerisation temperature is of 70° C. in all stages.

The polymerisation conditions, molar ratios of reactants, thecomposition of the copolymer produced in each stage and the compositionof the final polymer product and its properties are shown in Table 1.

The composition of example 1 and the one of the comparative example 1care utilised for preparing a bioriented triple-layer film having athickness of 25 μm. The layers are as follows:

a 1 μm-thick outer layer (layer A) is made up of a random copolymer ofpropylene containing 3.3 wt % and 6 wt % of recurring units derivingfrom ethylene and 1-butene, respectively;

the 23 μm-thick middle layer (layer B) is made up of a crystallinepropylene homopolymer;

the other outer 1 μm-thick layer (layer C) is made up of the compositionof example 1 or the one of the comparative example 1c.

The said three-layer film is prepared by coextrusion using a Brücknerextrusion system. Then the film is subjected to metallization processaccording to known methods wherein layer C is metallized with aluminium.

The film so obtained is subjected to the WVTR water vapour test and OTRoxygen test.

Table 2 shows the mechanical and physical properties of the films orplaques prepared with the compositions of the present invention.

TABLE 1 Example and comparative example 1c 1 2 Stage (i) Pressure (MPa)2.1 1.7 1.9 H₂/C₃ (mol) 0.046 0.017 0.015 C₄ ⁻/(C₄ + C₃) (mol) — — 0.06Copolymer (a) content¹⁾ (wt %) 66 35 35 1-butene content in copolymer(a) (wt %) 8.3 5.9 3.1 MFR “L” (g/10 min) 6.3 5.8 6.0 Stage (ii)Pressure (MPa) 2.1 1.9 1.9 H₂/C₃ ⁻ (mol) 0.077 0.060 0.053 C₄ ⁻/(C₄ ⁻ +C₃ ⁻) (mol) 0.15 — 0.23 Copolymer (b) content¹⁾ (wt %) 34 30 30 1-butenecontent in copolymer (b) (wt %) 10.4 12.2 15.4 MFR“L” (g/10 min) 5.8 7.15.2 Stage (iii) Pressure (MPa) — 1.9 1.9 H₂/C₃ (mol) — 0.064 0.057 C₄⁻/(C₄ ⁻ + C₃ ⁻) (mol) — 0.15 0.16 Copolymer (c) content¹⁾ (wt %) 0 35 351-butene content in copolymer (c) (wt %) 0 9.1 9.1 Final CompositionMFR“L” (g/10 min) 5.8 5.5 4.5 1-butene content (wt %) 9.0 8.9 8.9 Xylenesoluble fraction (wt %) 2.5 2.5 6.2 Melting temperature (° C.) 145 145151 Temperature at which 30% of the 117.5 118.5 120.0 composition ismelted (° C.) ¹⁾Copolymer content with respect to the final composition.

TABLE 2 Example and comparative example 1c 1 2 VICAT (° C.) 128 129 132SIT (° C.) 118 118 116 HDT 455 kPa (° C.) 73 71 72 Flexural elasticmodulus (MPa) 1080 1110 1140 RCI IZOD impact strength (kJ/m²) 5.3 6.46.9 Hardness Rockwell R (° R.) 100.8 102 101 Fish eyes >1.5 mm (n°/m²⁾ 00 0 Fish eyes 0.7-1.5 mm (n°/m²⁾ 2 1 0 Fish eyes 0.5-0.7 mm (n°/m²⁾ 7 42 Fish eyes >0.1 mm (n°/m²⁾ 500 270 250 Haze on 50 μm thick film (%) 1.71.6 1.5 Haze on 1 mm thick plaque (%) 34.7 35.0 36.7 Gloss 60° on 1 mmthick plaque (%) 83.0 84.8 84.5 Gloss 45° on 1 mm thick plaque (%) 58.059.6 59.6 WVTR water vapour (g/(m²·24 hours)) 0.25 — 0.17 OTR oxygen¹⁾(ml/(m²·24 hours)) 45 — 30 ¹⁾The test is carried out at ambienttemperature for a time of 20 minutes; the surface of the film sampleunder test is 5 cm².

What is claimed is:
 1. A semicrystalline polyolefin compositioncomprising (all percentages by weight): a) 25-40% of a random copolymerof propylene with at least one comonomer selected from C₄-C₁₀ α-olefins,containing from 2 to 10% of recurring units deriving from the comonomer;b) 25-40% of a random copolymer of propylene with at least one comonomerselected from C₄-C₁₀ α-olefins, containing from 10 to 20% of recurringunits deriving from the comonomer; c) 25-40% of a random copolymer ofpropylene with at least one comonomer selected from C₄-C₁₀ α-olefins,containing from 6 to 12% of recurring units deriving from the comonomer;where the total content of recurring units from the said comonomer,referred to the composition, is equal to or higher than 6% and therespective percentages representing the content of the said recurringunits in each one of copolymers a), b) and c) are different from eachone of the other two, said difference with respect to the percentage ofrecurring units in each one of the other two copolymers being of atleast 1 unit.
 2. The composition of claim 1, where the comonomer ofcopolymers (a), (b) and (c) is the same.
 3. The composition of claim 2,where the comonomer of copolymers (a), (b) and (c) is 1-butene.
 4. Thesemicrystalline polyolefin composition of claim 1, wherein the amount ofthe random copolymer (a) is 28-38%.
 5. The semicrystalline polyolefincomposition of claim 1, wherein the amount of the random copolymer (b)is 26-36%.
 6. The semicrystalline polyolefin composition of claim 1,wherein the amount of the random copolymer (c) is 28-38%.
 7. Thesemicrystalline polyolefin composition of claim 1, wherein thedifference with respect to the percentage of recurring units in each oneof the other two copolymers is of at least 1.5 units.